Mikola, et al., Plant and Cell Physiology 16, 933-937 (1957) disclose the sensitivity of the aleurone grains of oilseeds such as cottonseeds and peanuts to aqueous media.
U.S. Pat. No. 3,794,735, Newsom, et al., Feb. 26, 1974 discloses a method for isolating protein from protein bearing seeds without removing the lipid (defatting). An aqueous emulsion of protein and water is formed and centrifuged to remove cellulosic materials. The protein is recovered by isoelectric precipitation. R. D. Hagenmaier, J. Am. Oil Chem. Soc; 51, 470 (1974) discloses the preparation of sunflower seed isolate from full fat seeds by solubilization and extraction followed by isoelectric precipitation and centrifugation.
M. P. Tombs, Plant Physiology, 42, 797 (1967) describes a method of isolating protein bodies from soy meal by density gradient centrifugation using a 70% to 90% (wt/vol) aqueous sucrose solution having a density from 1.25 to about 1.34. The reference also describes the swelling and bursting of protein bodies when the meal is placed in contact with water, a problem which is said to be solved by buffering at pH 5, the isoelectric point of soy protein (glycinin).
K. Saio, D. Gallant, and L. Pettit, Cereal Chemistry, 54, 1171, (1977) disclose a method for recovering protein bodies from sunflower seeds. Defatted meal is suspended in a 20% sucrose solution buffered to pH 5 with citrate, sonicated, filtered through gauze, density fractionated in 70%-90% sucrose solution or in a 30%-90% sucrose gradient solution.
Certain other density fractionation-type processes for separating protein from other cellular materials are known. K. Saio and T. Watanabe, Agr. Biol. Chem., 30, 1133 (1966) disclose the recovery of protein bodies from soybeans by centrifugation in a cottonseed oil-carbon tetrachloride mixture after homogenizing milled seeds in the cottonseed oil. U.S. Pat. No. 3,828,017, Finely, et al. (1974) discloses the centrifugation of a slurry of pulverized soy material and liquid fluorocarbon having a density of 1.35 to 1.45. J. W. Finley, J. Food Sci., 41 882 (1976) discloses the use of chloro- and fluorocarbons in the density separation of protein from wheat flour. Systems such as Freon-11 with ethanol, acetone, hexane and ethyl acetate, and benzene with carbon tetrachloride are disclosed.
U.S. Pat. No. 3,365,440, Circle, et al., Jan. 23, 1968 discloses a process for leaching water soluble protein from soybeans through a countercurrent extraction with an aqueous solution buffered at the isoelectric point of soy protein which is alkali-soluble and acid-precipitable. The residue can be extracted with alkaline solution and acidified to recover an isolate.
U.S. Pat. No. 3,630,753, Melnchyn, Dec. 28, 1971 relates to the treatment of alkaline slurries of soy isolate to reduce viscosity.
Other methods for isolating protein have involved extraction of protein by solubilization in mixtures of polar and nonpolar solvents and dissolution followed by reprecipitation of protein. U.S. Pat. No. 2,278,670, Rauer, Apr. 7, 1942, discloses a two-step process for recovering protein using organic solvents and alkali.
U.S. Pat. No. 3,043,826, Beaber, et al., July 10, 1962 discloses the extraction of protein from alcoholtreated soybean material by contact with water at alkaline or acidic pH's and with subsequent recovery by precipitation.
Japanese Pat. No. 2,130,942, Ajinomoto, Apr. 22, 1976 (abstract) discloses the separation of protein material by isoelectric precipitation.
U.S. Pat. No. 4,072,671, Sodini, et al., Feb. 7, 1978 relates to the extraction of phenols and oligosaccharides from vegetable materials using a polar organic solvent, especially n-butanol, combined with an aqueous solution of an acidic electrolyte, especially hydrochloric acid.
Other separation procedures are also known. U.S. Pat. No. 3,734,901, Hayes, et al., May 22, 1973 discloses a protein concentration step in which nonproteinaceous materials are separated from vegetable seed material using a monohydric alcohol/water extraction medium. U.S. Pat. No. 3,649,293, Hoer, et al., Mar. 14, 1972 teaches the separation of protein by solubilizing the protein, deposition the protein on solid cellular material, and separating the protein-carrying solids, which are processed further.
Still other procedures involve the use of aqueous polyelectrolyte solutions, e.g. carboxymethylcellulose, carrageenan, guar gum, and sodium alginate to obtain concentrates, U.S. Pat. No. 3,762,929, Delapp, Oct. 2, 1973; to improve the water solubility of globulins, U.S. Pat. No. 3,407,076, Ganz, Oct. 22, 1968; to recover solubilized protein from whey, U.S. Pat. No. 3,069,327, Eldridge, et al., Dec. 18, 1962 and U.S. Pat. No. 3,792,175, Schmidt, Feb. 12, 1974; and to prepare water soluble complexes of water dispersible protein, U.S. Pat. No. 3,842,062, Eastman, Oct. 15, 1977.